Signaling through receptor tyrosine kinases is known to initiate a number of cellular events, and when deregulated are associated with many different disease states including cancer. Phosphoinositide 3-kinase (P13K) has been shown to be a major signaling protein downstream of tyrosine kinase receptors, although its direct targets have remained elusive. Protein kinase B, or c-akt, is a proto-oncogene that is amplified in a number of human tumors, and is activated by growth factors in a P13K-dependent manner. P13K itself is also increased in copy number in ovarian cancers. The importance of this pathway in tumor formation is suspected to be due to increasing cell survival,presumably through phosphorylation of the protein BAD by PKB. Recently, we identified and characterized a novel protein kinase termed phosphoinositide-dependent kinase-1 (PDK-1), which mediates the activation of PKB by P13K. The products of P13K act on this pathway by both activating PDK-1, and priming PKB for phosphorylation by PDK-1. This research proposal seeks to further characterize the role of PDK-1 in this pathway, to determine whether its activity is modulated in a growth factor-dependent manner, to see if its activity is required for PKB activation under a set of different conditions, and to screen for additional substrates of this kinase (Aim 1). The second aim will address whether intramolecular interactions play a role in suppressing the activity of PKB under non-stimulating conditions, and ask whether additional proteins are involved in PKB activation. Finally the activity of the P13K/PKB pathway will be analyzed in a number of different tumor cells to determine the proportion of tumors containing elevated activity. The effect on tumorigenesis of inhibiting this pathway will also be examined (Aim 3).